1. Field of the Invention
The present invention relates to a liquid cooled rotor type rotary electric machine whose rotor is cooled by circulating a cooling liquid therein. More particularly, the invention relates to a device for conducting the cooling liquid out of the machine.
2. Description of the Prior Art
As is well known in the art, any increase of the capacity of a rotary electric machine depends on the ability to suppress increases in the temperature thereof, that is, how to effectively cool the machine. In other words, the maximum permissible capacity of a rotary electric machine is determined by its maximum temperature and hence its ability to dissipate heat. On the other hand, there have been strong demands for increased capacity of rotary electric machines including electric generators and especially turbine generators in order to improve the efficiency of power plants. For this purpose, a cooling technique of circulating hydrogen gas for cooling a turbine generator has been employed thus increasing the capacity thereof. However, this technique appears to have met its limit for increased capacity. Accordingly, it is necessary to provide another suitable cooling technique.
In order to meet this requirement, a technique has been proposed in which, instead of hydrogen gas, a cooling fluid such as water which is high in cooling efficiency is employed as the cooling medium. According to this technique, a cooling liquid is circulated in the stator to cool the latter. If this technique could be developed satisfactorily to cause the cooling liquid to circulate not only in the stator but also in the rotor, then the cooling effect would be greatly improved.
For instance, in the case of a turbine generator, its rotor rotates at a high speed of 3600 rpm. (60 Hz). Therefore, the forcing of the cooling liquid through the desired paths in high-speed rotating element is a problem the solution of which is considerably difficult. This difficult problem has retarded the commercialization of liquid cooled rotor type rotary electric machines.
FIG. 1 shows a device for directing the flow of cooling liquid in a liquid cooled rotor to which the technical concept of the invention is applicable. In FIG. 1, a reference numeral 1 designates an inlet pipe through which a cooling liquid such as pure water is supplied with the aid of a supply pump (not shown), 2 a cylindrical liquid inflow pipe for receiving the cooling liquid from the inlet pipe 1 through an opening 2a with the hollow interior 2b forming the inflow path of the cooling liquid, and 3 a liquid outflow pipe placed over the inflow pipe 2 with a gap 3b providing a predetermined clearance therebetween. Pure water is preferred so as to not corrode any of the pipes with impurities. The gap 3b is utilized as the outflow path of the cooling liquid. The outflow pipe 3 has an opening 3a through which the cooling liquid is discharged. The outflow pipe 3 and the inflow pipe 2 are connected together to form a cooling liquid supplying and draining pipe 4 as shown in FIG. 2. As is apparent from FIG. 2, the inflow pipe 2 has a plurality of (six in the case of FIG. 2) protruding pieces 2c extending from the outer wall of the pipe 2. The protruding pieces 2c serve as spacers which couple the inflow pipe 2 and the outflow pipe 3 together and reinforce the pipes 2 and 3. The inflow pipe 2 with the protruding pieces 2c is made integral with the outflow pipe 3, for instance, by shrink fitting, to form the supplying and draining pipe 4. The pipe 4 has a flange 4a at its end which is coupled to the flange 5a of the shaft of the rotor of a rotary electric machine with bolts or the like (not shown). The rotor coil (not shown) is mounted on the shaft 5. As is clear from FIG. 1, a inflow path 5b and a outflow path 5c are formed in the rotor shaft 5 and are communicated with the inflow path 2b and the outflow path 3b in the supplying and draining pipe 4, respectively, so that the cooling liquid supplied through the inflow path 5b, after circulating in the rotor coil, is discharged into the outflow path 5c. In FIG. 1, the arrows indicate the flow of the cooling liquid. As described above, the cooling liquid, after cooling the rotor coil by circulating therein, is drained from the opening 3a of the outflow pipe 3 through the outflow paths 5c and 3b.
The device has a first outlet chamber 61 for receiving the liquid discharged from the opening 3a. The chamber 61 is so designed that it is always filled with the cooling liquid in order to prevent contamination of the cooling liquid (pure water) which might occur if the liquid were to be brought into contact with the atmosphere. The first outlet chamber 61 has a first outlet pipe 71 for conducting the cooling liquid out of the chamber 61. The cooling liquid discharged from the first outlet pipe 71 is not brought into contact with atmospheric air, that is, it is prevented from being contaminated, and therefore it can be resupplied to the inlet pipe 1 through a supply pump (not shown) after its temperature is decreased by a heat exchanger or the like (not shown). That is, the water can be recirculated.
In FIG. 1, reference numeral 81 designates a first labyrinth seal for preventing the leakage of cooling water from the inlet pipe 1 into the first outlet chamber 61. It is impossible to completely eliminate the leakage of liquid between a stationary part and a rotary part, but it is necessary to make maximum efforts to prevent the leakage of liquid. The liquid leaked into the chamber 61 will cause no serious difficulty because it is recirculated through the outlet pipe 71. However, it goes without saying that the amount of leaked liquid should be as small as possible because, if it is excessively large, the efficiency of the device is decreased.
A second labyrinth seal 82 is provided to prevent the leakage of liquid between the first outlet chamber 61 and the rotating pipe 4. A second outlet chamber 62 is provided for receiving the liquid which leaks through the second labyrinth seal 82 from the first outlet chamber 61. In the second outlet chamber 62, unlike the first outlet chamber 61, the cooling liquid is not fully filled therein and therefore the cooling liquid may be contaminated by contacting the air. In order to prevent this, a gas supplying pipe 9 is provided. Shielding gas such as nitrogen or hydrogen is supplied into the second outlet chamber 62 through the gas supplying pipe 9 at all times so that the pressure in the second outlet chamber 62 is maintained slightly higher than the ambient atmospheric pressure thereby preventing the entry of air into the second outlet chamber 62. Thus, the liquid leaked into the second outlet chamber 62 is not brought into contact with atmospheric air and accordingly not contaminated. Therefore, the cooling liquid discharged from the second outlet pipe 72 of the chamber 62 can be recirculated through a heat exchanger and a supply pump (none of which are shown) as in the case of the cooling liquid discharged from the first outlet chamber 61.
Further to FIG. 1, reference numeral 83 designates a third labyrinth seal for preventing the leakage of liquid between the second outlet chamber 62 and the rotation pipe 4. A sealing liquid at a slightly higher pressure than the shielding gas is supplied from a liquid supplying pipe 83a to the middle portion of the labyrinth seal 83. A part of the sealing liquid flows into the second outlet chamber 62 through a labyrinth seal 83c. As described above, the cooling liquid from the second outlet pipe 72 is recirculated without being subjected to water purifying treatment. Therefore, the sealing liquid must be pure water, substantially the same as the cooling liquid.
Yet further in FIG. 1, reference numeral 63 designates a third outlet chamber for receiving sealing liquid which has passed through the labyrinth seal 83b, and 73 a third outlet pipe communicating with the third outlet chamber 63. Since the third outlet pipe 73 communicates with the atmosphere, sealing liquid leaked into the chamber 63 is contaminated and therefore it is discarded without being recirculated. It goes without saying that if it is supplied to a retreatment device for water purification, it can be recirculated.
As described above, the sealing liquid (pure water) leaked into the third outlet chamber 63 is discarded or reprocessed. Therefore, in order to make the required capacity of the pure water supply or the size of the retreatment device as small as possible it is necessary to minimize the amount of sealing liquid leaked into the third outlet chamber.
A part of the conventional third seal 83, namely, a seal 83b disposed on the side of the third outlet chamber, 63 is a labyrinth seal. It is necessary to increase the length of the sealing part in order to minimize the amount of sealing liquid leaking into the third outlet chamber 63. On the other hand, because the rotor shaft 5 is supported by bearings (not shown), it is impossible to provide bearings for the supplying and draining pipe 4 because of the presence of the outlet chambers, and accordingly the pipe 4 is supported hanging over the rotor shaft 5. This results in lateral vibration of the pipe 4 continuously. Such lateral vibration is undesirable because it disturbs the sealing effect. Lateral vibration tends to increase as the length of the pipe 4 increases. Thus, it is desirable to make the pipe as short as possible. The above-described conventional device suffers from a problem in that the sealing effect cannot be increased without increasing the third seal's length and, accordingly, the length of the pipe 4. If the length of the third seal and accordingly the pipe 4 are increased, undesirable lateral vibration is increased accordingly.
Thus, it is necessary to provide a cooling liquid conducting device which is compact and has only a small lateral vibration in which the seal 83b disposed on the side of the third outlet chamber 63 is replaced by a seal which is shorter but more effective in sealing thereby minimizing the amount of sealing liquid leaking into the third outlet chamber 63.
In order to eliminate the necessity of increasing the size of a pure water manufacturing device or capacity of pure water supply, a method has been employed in which threads are cut in the outer wall of the supplying and draining pipe in a direction opposite to the direction of rotation of the pipe so that a pumping effect is provided by the threads and the confronting stationary surface 85 during high speed rotation thereby to minimize the amount of sealing liquid leaking into the third outlet chamber 63.
However, the conventional seal is disadvantageous in that when the supplying and draining pipe is stopped or when the rotational speed of the supplying and draining pipe 4 is low and accordingly the pumping effect is insufficient, a large amount of sealing liquid leaks into the third outlet chamber containing air. In this connection, the capacity of the sealing liquid supplying device must be determined from the amount of sealing liquid leakage when the pipe is stopped or run at low speed, and therefore the leakage of sealing liquid when the pipe is stopped or run at a low speed is the primary difficulty of the conventional seal.
Not only the above-described threads but also any structure in which sealing is effected by the pumping effect which is provided due to rotation suffers from a common difficulty that the sealing effect is lost or lowered when the pipe is stopped or run at a low speed.
As is apparent from the above description, the seal utilizing the pumping effect through rotation is advantageous in that it is contactless and is effectively operable even when the circumferential speed is high and vibration is present but is disadvantageous in that its sealing effect is greatly lowered when the supplying and draining pipe is stopped or run at a low speed.